Electric circuit interrupter of the vacuum type with series-related arcing gaps



May 25, 1965 c, rrus 3,185,798

ELECTRIC CIRCUIT INTERRUPTER OF THE VACUUM TYPE WITH SERIES-RELATED ARCING GAPS Filed 001;. 8, 1962 /IYIIIIII/II,

//vv/v TOR. CHARLES H 77mm,

ATTORNEY.

United States Patent 3,185,798 ELECTRIQ CIRCUET INTERRUPTER fill THE VA CUUll l TYPE WETH SERIES-RELATED ARCING GAPS Charles H. Titus, Newtown Square, Pa, assignor to General Electric Company, a corporation of New York Filed Oct. 8, 1962, Ser. No. 228,799 11 (Ilaims. (Cl. Edit-"144) This invention relates to an electric circuit interrupter of the vacuum type and, more particularly, to a circuit interrupter that comprises electrode structure forming a pair of series-related arcing gaps.

When the interrupter is opened to initiate a circuitinterrupting operation, series-related arcs are established across the arcing gaps, after which these arcs are preferably spun in a circumferential direction about the axis of the interrupter until extinguished. Prior interrupters of this general nature have typically been subject to the disadvantage that, when open, they contain regions that are unduly susceptible to the type of spark breakdown that can result in a power are extending between the terminals of the interrupter and shorting out the seriesrelated gaps. If the initial spark had occurred across only one of the series-related gaps instead of across the space bridging the two gaps, there would be an excellent chance that the spark would be extinguished before the other gap could break down, thus preventing the establishment of a power are or the flow of any power follow current between the terminals of the interrupter.

Accordingly, an object of the present invention is to construct the electrode structure in such a manner as to minimize the chances for the occurrence of a spark that could result in a single power are shorting out the seriesrelated gaps.

Another object is to force substantially all spark breakdowns that do occur to occur across one of the seriesrelated arcing gaps instead of between parts electricallyconnected to the opposite terminals of the interrupter.

In a vacuum-type interrupter it is customary to provide vapor-condensing shielding to condense the metallic vapors generated by arcing. Such condensation by the shielding not only protects the insulation of the interrupter from being coated and thus impaired by the metallic particles contained in the vapors but also reduces the chances that such vapors will induce a breakdown across an electrically stressed region of the interrupter.

Another object of my invention is to design the electrode structure in such a manner that it is capable itself of serving as the primary vapor-condensing shielding of the interrupter.

In a preferred embodiment of the invention, the interrupter has multiple contact points connected in parallel to render it suitable for high continuous and momentary current-carrying duty. Another object of my invention is to construct the electrode structure in such a manner that the forces present at these multiple contact points tend to balance out each other, thus reducing the ct forces on the supports of the electrode structure.

In carrying out my invention in one form, I provide a pair of cup-shaped electrodes, each comprising a body portion and a tubular skirt projecting from said body portion and terminating in an outer end of annular configuration. These electrodes are mounted in spaced-apart relationship with the skirts generally aligned and the outer ends spaced from each. Each of the cup-shaped electrodes further comprises a tubular arc-running portion located radially inwardly of the skirt and means electrically interconnecting the skirt and the tubular arcrunning portion in such a manner that current flowing between the tubular arc-running portion and the skirt is 3,185,798 Fatented May 25, 1965 forced to flow through said outer end. Between the cupshaped electrodes and electrically-insulated therefrom when the interrupter is open, is an intermediate electrode that has two axially-extending portions respectively located radially inwardly of the tubular arc-running portions of the cup-shaped electrodes. There are annular spaces between each of the axially-projecting portions and the tubular arc-running portions that constitute series-related arcing gaps. When the interrupter is closed, current is conducted between the two cup-shaped electrodes by contact means that can be moved toward an open position to establish a pair of series-related arcs in an arc-initiation region adjacent the outer ends of the skirts. Means is provided for driving these arcs in a radially inward direcion from said arc-initiation region into said series-related arcing gaps. In a preferred embodiment of the invention, means is provided for propelling the arcs in a circumferential direction about the axially-projecting portions of the intermediate electrode when the arcs have reached the series-related arcing gaps.

For a better understanding of the invention, reference may be had to the following description taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a side elevational view partially in section illustrating a vacuum interrupter embodying one form of my invention.

FIG. 2 is an enlarged detailed view of a portion of the interrupter of FIG. 1.

FIG. 3 is a sectional view taken along the line 3--3 of FIG. 1.

FIG. 4- illustrates a modified form of the invention.

Referring now to FIG. 1, there is shown a vacuumtype circuit interrupter comprising an evacuated envelope ill. This envelope 10 comprises a cylindrical casing 11 primarily of glass or other suitable insulating material and a pair of metallic end plates 12 and 13 disposed at opposite ends of the casing 11 and joined thereto by means of suitable vacuum-type seals 14. The casing 11 preferably comprises a pair of coaxially disposed glass cylinders 11a and 11b and an intermediate metallic cylinder 11c disposed therebetween in coaxial relationship to the glass cylinders. Suitable vacuum tight seals are provided between the glass cylinders 11a, 11b, and the metallic cylinder 11c.

Disposed within the evacuated envelope 10 is a pair of cup-shaped electrodes 17 and 18. Each of these electrodes has a body portion 19 of disc form and a tubular skirt 2!) projecting from the body portion 19 and terminating in an outer end 22 of annular configuration. As shown in FIG. I, the skirt portions 2% of the two electrodes are disposed in substantially aligned relationship, and their outer ends 22 are spaced apart along the longitudinal axis of the envelope 10.

Each of the cup-shaped electrodes 17 and 18 also comprises a tubular arc-running portion 24 integrally-joined to the tubular skirt portion lit and located radially inwardly of the skirt portion in generally concentric relationship with the skirt portion. The only electrical connection between the tubular skirt portion 20 and the tubular arc-running portion 24 is through the free end 22 of the cup-shaped electrode. As a result, any electrical current flowing between the skirt 2t) and the are running portion 24 is forced to flow through the outer end of the electrode. The importance of this relationship will soon be described in greater detail.

The upper electrode 17 is mounted in the abovedescribed fixed position Within'the envelope 10 by means of a conductive rod 26 that is suitably joined, as by brazing, at its upper end to the upper end cap 12 and at its lower end to electrode 1'7. The lower electrode 13 is similarly supported by means of a second conductive rod 28 s ear/ea that is suitably joined at its upper end to the electrode and at its lower end to the end cap 13.

The space between the adjacent ends of the two cupshaped electrodes 17 and 18 is bridged by means of a pair of movable contacts 39 and 32. One of these contects is mounted on the inner end of a conductive operating rod 34 projecting radially through the insulating casing 11. The other contact 32 is mounted on the inner end of a similar conductive rod 35 projecting radially through the casing 11 at a point diametrically opposed to the position of the first rod 34. Each of these conductive rods 34 and 36 is surrounded by a flexible metallic bellows 35 that provides a vacuum-tight seal about the rod and permits movement of the rod with respect to the casing 11 without impairing the vacuum inside the casing.

Preferably each of these conductive rods 3 and is provided with a guide such as 37 that provides some guidance of the rod as it moves longitudinally during opening or closing action. The guide 37 does, however, allow enough movement of the rod 34 in a radial direction to permit the contact 39 to firmly seat against both electrodes 17 and 13 upon closing. In this regard, if the contact 39 upon closing should first engage one of the electrodes a slight amount of pivoting would be necessary to firmly engage the other electrode. The bearing 37 is designed to permit such slight pivotal motion. Along these same lines, the contact-operating means (not shown) is suitably designed to permit such slight pivotal motion.

When the contacts are in their closed position shown,

electric current can flow through the interrupter between I an upper terminal 39a and the lower terminal 3% via a path that extends through the upper end cap 12, rod 25, electrode 17, bridging contact 3t) or 32, electrode 18, rod 28, and lower end cap 18. Opening of the interrupter is effected by simultaneously driving the operating rods 34 and 36 radially outward to separate the bridging contacts '30 and 32 from the electrodes 17 and 18, thereby establishing a gap between the electrodes 17 and 18 and between each electrode and the bridging contacts. Closing of the interrupter is effected by simultaneously driving the rods 34 and 36 radially inwardly to return the contacts 349 and 32 to their illustrated position of engagement with electrodes 17 and 18.

Disposed between the two cup-shaped electrodes 17 and 13 is an intermediate electrode 46 comprising two rings, each of a generally L-shaped cross section and having a horizontal leg 43 disposed in generally parallel back-to-back relationship with the horizontal leg of the other ring. These horizontal legs 43 are integrally joined together at the radially outermost region of the intermediate electrode 4tl about the outer periphery of the intermediate electrode. The horizontal legs 43 of the L-shaped rings are located between the free ends of the cup-shaped electrodes 17 and 1S and extend radially therebetween to a position located radially beyond the outermost periphery of the cup-shaped electrodes 17 and 18. The remainder of each L-shaped ring comprises a tubular portion 44 located radially inwardly of the arc-running por tion 24 of the cup-shaped electrode and disposed in generally concentric, spaced-apart relationship with this arcrunning portion 24. The annular space between each tubular portion 44 and the surrounding arc-running portion 24 of the cup-shaped electrode constitutes an arcing gap 46, as will soon be explained.

The intermediate electrode is interposed in all straight line paths extending between the two cup-shaped main electrodes 17 and 18. Along these lines, note that there is an imperforate barrier 47 that extends diametrically across the centrally-located tubular region of the electrode 4-0. Note also that the horizontally-extending legs 43 of the L-shaped annular rings project radially outward well past the outermost periphery of the two electrodes 17 and 18. Thus, any straight line path interconnecting the two electrodes 17 and 11% will be intersected by either the central barrier 47 or the L-shaped cross-section annular rings. The presence of the intermediate electrode 4% in all of the straight line paths greatly reduces the possibility that any spark breakdowns bypassing the intermediate electrode 49 will occur between the two cupshaped electrodes 17 and 18 when the interrupter is open. Any spark breakdowns that do occur from one of the electrodes 17 or 13 will be to the intermediate electrode 4d rather than directly to the other main electrode. This spark breakdown will generally be extinguished in the vacuum of the interrupter before any additional breakdown can take place between the intermediate electrode and the other main electrode, thus preventing any power are from being established as a result of the initial spark breakdown.

The intermediate electrode 40 is supported in its illustrated position by means of angular spaced metallic pins 49 projecting radially-inwardly from the metallic intermediate portion itlc of the casing 11. These pins 49 can best be seen in the sectional view of FIG. 3. These pins 49 at their inner ends are suitably connected to the outer periphery of the intermediate electrode 49 and at their outer ends are suitably connected to the metallic cylinder 11c. Since the contacts 3% and 32 are also electrically connected to the cylinder 110, as indicated at 53, it will be apparent that the contacts 353 and 32 and the intermediate electrode lil are always at the same potential.

When the movable bridging contacts 3% and 32 are driven radially outward to open the interrupter, two seriesrelated arcs are established at one of the two contacts. Assuming the arcs are drawn at contact 3%), one of these arcs is between the upper electrode 17 and the upper projecting portion of the bridging contact 3t and the other between the lower electrode 18 and the lower projecting portion of the bridging contact 3%. FIG. 2 illustrates these arcs at 5i and 51 immediately after they are established by bridging contact 30 during an opening operation. As soon as these arcs are established, they are driven radially inwardly from the arc-initiation region in which they are shown, into positions across the arcing gaps 46 located internally of the cup-shaped electrodes 17 and 18.

The force for driving the arc in this manner results from the illustrated loop-shaped configuration of the current path L through the contacts. As is well known, the magnetic effect of such a loop-shaped path is to lengthen the loop, and this tends to drive the arcs 5t) and 51 to the left. The upper terminal of arc 5t responds to this driving action by running to the left along the arc-running portion 24, and the lower terminal of the arc responds by running to the left along the inwardly projecting end of the movable contact until it jumps to the intermediate electrode 40. Thereafter the lower terminal continues moving to the left, running up the tubular portion 44 until the arc 5i has reached the position depicted at 58a. The lower arc 51 is driven radially inward in a similar manner into its position depicted at 51a.

As the arcs move toward their respective positions 56a and 51a, they are subjected to an additional magnetic force component that drives them circumferentially about the outer peripheries of the tubular portions 44 until they are extinguished and the circuit interrupted. This additional magnetic force component is derived from a series of skewed slots as that extend axially inward from the axially outermost ends of the tubular portions 44. These skewed slots 69 in effect divide the periphery of the tubular portion 44 into a series of angularly-spaced fingers 61 respectively located between adjacent slots 60. Each of these skewed slots has a circumferentially-extending component that forces current flowing to an arc terminal located on any of the fingers dll to follow a path that has a net component extending in a circumferential direction of the tubular portion 44. The magnetic effect of current flowing through such a circumferentially-extending path is to drive the arc in a circumferential direction about the external periphery of the tubular portion 44'. This circumferential motion of the arcs help to reduce arc erosion and to lessen the amount of vapors generated by the arcs, and this leads to improved current-interrupting ability.

The magnetic force for driving the arc circumferentially is preferably augmented by the provision of similar slots 64 provided in the tubular arc-running portion 24 of the two main electrodes 17 and 18. These slots 64 act in the same manner as slots 60 to force the current flowing adjacent an arc terminal to follow a path having a net circumferential component, the magnetic effect of which is to drive the are terminals circumferentially.

As is well known, arcing tends to release any gases that might be present in the parts that are subjected to arcing. It is therefore most important that the two main electrodes 17 and 18 and the intermediate electrode 40 have a high degree of freedom from sorbed gases and other gas-forming contaminants in order to prevent any such gases from impairing the vacuum during critical portions of the interrupting period. This freedom from sorbed gases and gas-forming constituents is obtained by suitable vacuum-processing techniques such as the zone-refining process described and claimed in application Serial No. 146,2415-Hebb, filed October 19, 1961, and assigned to the assignee of the present invention.

It will be noted that the arcing gaps 46 are virtually surrounded by the two cup-shaped electrodes 17 and 18. Thus, most of the metallic vapors generated by arcing are intercepted by and condensed on the internal walls of the two cup-shaped electrodes. The amount of current an interrupter can interrupt is directly dependent upon the efficiency with which the metallic vapors are condensed. The greater the quantity of vapor particles that are permitted to bounce olf the shielding, the greater the likelihood that these vapor particles will trigger an electrical breakdown across an electrically stressed region of the interrupter. The cup-shaped electrodes 17 and 18 are exceptionally efficient vapor condensers because they are of a relatively thick-Walled construction. This relatively large wall thickness helps the cup-shaped electrodes to remain cool and this, in turn, improves the vapor-condensing abilities of the wall.

The required wall thickness of the cup-shaped electrodes 17 and 18 is dictated primarily by mechanical strength and current-carrying capacity considerations. These latter considerations necessitate walls of considerable thickness inasmuch as the interrupter is intended for high current duty and high contact pressures and inasmuch as the cup-shaped electrodes are main current carrying parts that are exposed to full contact pressure. Thus, even apart from vapor-condensing considerations, walls of relatively great thickness are required for the cup-shaped electrodes. By utilizing these walls to perform the additional function of vapor-condensing, I am able to capitalize more completely on the relatively great wall thickness which is desirable for these other considerations.

Another factor that contributes to the eiiiciency of the cup-shaped electrodes as vapor-condensing shields is their previously-described high degree of freedom from sorbed gases and other gas-producing contaminants. Thus, despite bombardment of the cup-shaped electrodes by the hot arcing vapors, there is littlelikelihood that any permanent gases will be released or otherwise derived from the electrodes when they are acting in their shielding capacity. Thus, I am able to derive additional benefits from the high degree of gas-freedom that the electrodes 17 and 18 have.

Another factor that contributes to the high currentinterrupting capacity of the illustrated interrupter is the fact that a large percentage of the arcing vapors are forced into regions of low electric field strength. In this I respect, the skirts 20 of the cup-shaped electrodes are made relatively long so that there are relatively large regions adjacent the inner surfaces of the cup-shaped electrodes that are only weakly stressed by the electric field. By forcing most of the arcing vapors into these regions of low electric stress, the chances that they will trigger a dielectric breakdown after interruption at the first current zero are materially reduced.

Another important purpose of the shielding in a vacuum interrupter is to prevent the arcing vapors from reaching the insulation of the interrupter so as to prevent the vapors from condensing on the insulation and thus impairing it. The cup-shaped electrodes. are interposed between most of the arcing regions of the interrupter and its insulation, and thus are capable of providing a substantial amount of protection for the insulation. Some arcing vapors will, however, be genera-ted while the arcs are still outside of the cup-shaped electrodes 17 and 18, and most of these vapors will escape interception by the cup-shaped electrodes. To prevent such vapors from reaching the insulating casing 11, a metallic tubular shield 66 is provided just inside the insulating casing 11. This metallic shield 66 acts in a known manner to intercept and condense vapors emanating from the arcing regions of the interrupter and escaping the cup-shaped electrodes 17 and 18 before such vapors can reach the insulating casing. The shield 66 is supported on the intermediate portion of the insulating casing by suitable pins 67 projecting from this intermediate portion and suitably secured to the shield 66. The shield 66 is preferably maintained at substantially the same potential as the movable contact 30 by virtue of the conductive connection provided by the pins 67. The shield 66 has a pair of openings 68 that closely surround the operating rods 36 and 34 respectively. The operating rods are free to move within these openings 68 along their longitudinal axis during circuit opening and circuit closing operations. A metallic shielding disc 69 is preferably attached to each rod in alignment with opening 68 to condense any arc-generated vapors that happen to pass through the opening. a

An advantage of the illustrated interrupter is that most of the current-carrying and arcing parts of the interrupter can be made quite large and massive without necessitating the movement of large masses in opening and closing the interrupter. In this respect, note that in the illustrated embodiment the electrodes 17, ISand 44 are quite large and massive, but there is no need to move these parts in order to control the interrupter. The only parts that it is necessary to move are the relatively light bridging contacts 30 and 32. The low massof these parts enables a relatively small and expensive operating mechanism to be relied upon for operating the interrupter.

The massiveness of the electrodes 17 and 1S enables high continuous current to be carried by the interrupter without overheating. Furthermore, the heat resulting from these high currents or from arcing can be readily transmitted through these parts to the exterior of the casing 10 in View of the high thermal conductivity of these parts and the joints that interconnect them. As a further aid in dissipating heat from the interior of the interrupter, the conductive rods 34 and 36 on which the bridging contacts are mounted provide paths of low thermal impedance leading to the outside of the interrupter from the contact-making and breaking regions of the interrupter.

The two bridging contacts 30 and 32 provide parallel contact points through which current can be carried between the two main electrodes 1'7 and 18 and this adapts the interrupter for higher continuous and momentary currents than it could handle with a single bridging contact. Since the forces urging the two contacts into their closed position shown act on diametrically-opposed sides of the cup-shaped electrodes 17 and 18, it will be apparent that these forces tend to cancel out each other and to produce little resultant force on the supports 26 and 27 of the cup-shaped electrodes. In addition, since the bridging contacts Siland 32 do not engage the intermediate electrode 40 at all, this electrode 40 receives none of the contact forces, thus permitting its support to be of reduced size and strength.

s eaves FIG. 4 illustrates a modified embodiment of my invention wherein each of the arcs established across an arcing gap 56 is subdivided into two series-related arcs. The means for subdividing each of the arcs comprises a metallic disc 7% having an annular flange 72 projecting therefrom into the annular space adjacent the ends of the arc runners 24 and 44. When an arc is driven radially inwardly into this region, as previously described, it engages the annular flange '72 and is thus split into two series-related arclets as shown at 75 and '76. This subdivision of each are into two arclets provides a total of four arclets in series, and this larger number of arcs in series enables the interrupter to handle higher voltages than it could otherwise handle.

An annular disc '70 is provided within each of the two cup-shaped electrodes 1'7 and 18 and is supported within its respective electrode by a suitable insulator 78. This insulator is protected from vapor condensation by shielding means comprising a pair of concentric spacedapart metallic cylinders 79 and 89. One of the cylinders '79 is carried by the disc 70 and the other 3% by the cup-shaped electrode. The cylinders axially overlap to present a tortuous path to any vapors traveling toward the insulator 78.

While I have shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made Without departing from my invention in its broader aspects, and I, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A vacuum-type circuit interrupter comprising:

(a) a pair of cup-shaped electrodes, each comprising a body portion and a tubular skirt projecting from said body portion and terminating in an outer end of annular configuration,

(1)) means for mounting said electrodes in spacedapart relationship with said skirts generally aligned and said outer ends spaced from each other,

(c) each of said cup-shaped electrodes further comprising a tubular arc-running portion located radially inwardly of said skirt and means electrically interconnecting said skirt and said tubular arc-running portion in such a manner that current flowing between said tubular arc-running portion and said skirt is forced to flow through said outer end,

(:1) an intermediate electrode having two tubular portions,

(e) means for electrically insulating said intermediate electrode from said cup-shaped electrodes when said interrupter is open and for mounting said intermediate electrode in such a position that its tubular portions are respectively located radially inwardly of the tubular arc-running portions of said cup-shaped electrodes with annular spaces therebetween constituting series-related arcing gaps,

(1) contact means operable in a closed position to conduct current between said cup-shaped electrodes and movable toward an open position to establish a pair of series-related arcs in an arc-initiation region adjacent the outer ends of said skirts,

(g) and means for driving said arcs in a radially-inward direction from said arc-initiation region into said series-related arcing gaps.

2. The circuit interrupter of claim 1 in combination with means for propelling the arcs in a circumferential direction about the tubular portions of the intermediate electrode when the arcs have reached said tubular portions.

3. The interrupter of claim 1 in which substantially all straight line paths extending between said two cupshaped electrodes when said interrupter is open are intersected by said intermediate electrode.

4. The interrupter of claim 1 in which said intermedi- 8 ate electrode further comprises an annular portion that extends radially outwardly from said tubular portions past the outer periphery of said cup-shaped electrode so as to intersect straight-line paths extending between said cup-shaped electrodes at their outer ends.

5. The interrupter of claim 4 in which said intermediate electrode comprises a substantially impertorate barrier extending across the space surrounded by the tubular portions of said intermediate electrode so as to intersect straight line paths extending between said cup-shaped electrode internally of said tubular portions.

6. The interrupter of claim 1 in combination with arcsplitting means for splitting the are drawn at each of said arcing gaps into two series-related arclets.

7. The interrupter of claim 1 in combination with arc splitting means for splitting the arc drawn at each of said arcing gaps into two series-related arclets, said arcsplitting means for one of said arcing gaps comprising an annular ring within one of said cup-shaped electrodes and insulating means for supporting said annular ring on said one cup-shaped electrode.

8. A vacuum type circuit interrupter comprising:

(a) a pair of cup-shaped electrodes, each comprising a body portion and a tubular skirt projecting from said body portion and terminating in an outer end of annular configuration,

(b) means for mounting said electrodes in spaced-apart relationship With said skirts generally aligned and said outer ends spaced from each other,

(0) movable contact means having a closed position engaging said skirts and bridging the space between the outer ends of said two electrodes,

(d) said movable contact means being movable radially outwardly with respect to said cup-shaped electrodes into an open position to establish series-related arcs, one are between one of said cup-shaped electrodes and said movable contact and the other are between the other of said cup-shaped electrodes and said movable contact,

(e) an intermediate electrode disposed between said two cup-shaped electrodes and defining with said cup-shaped electrodes series-related arcing gaps located radially inwardly of said tubular skirts, and

(1) means for forcing said arcs into said arcing gaps.

9. A vacuum-type circuit interrupter comprising:

(a) a cup-shaped electrode comprising a body portion and a tubular skirt projecting from said body portion and terminating in an outer end of annular configuration,

(b) said cup-shaped electrode further comprising a tubular arc-running portion located radially inwardly of said skirt and means electrically interconnecting said skirt and said tubular arc-running portion in such a manner that current flowing between said tubular arc-running portion and said skirt is forced to flow through said outer end,

(c) a second electrode having a tubular portion,

(d) means for electrically insulating said second electrode from said cup-shaped electrode when said interrupter is open and for mounting said second electrode in such a position that its tubular portion is located radially inwardly of the tubular arc-running portion of said cup-shaped electrode with an annular space therebetween defining an arcing gap,

(e) movable contact means having a closed position engaging said skirt and movable with respect to said cup-shaped electrode to establish an arc in an arcinitiation region adjacent the outer end of said skirt, and

(f) means for driving said are in a radially-inward direction from said arc-initiation region into said areing gap.

10. A vacuum type circuit interrupter comprising:

(a) a pair of main electrodes, each comprising a body portion and a tubular skirt projecting from said body portion and terminating in an outer end of annular configuration,

(b) means for mounting said main electrodes in spacedapart relationship with said skirts generally aligned and said outer ends spaced from each other,

(0) each of said main electrodes further comprising a tubular arc-running portion located radially inwardly of said skirt and means electrically interconnecting said skirt and said tubular arc-running portion in such a manner that current flowing between said tubular arc-running portion and said skirt is forced to flow through said outer end,

(0.) an intermediate electrode having a central portion and two other portions projecting from said central portion in opposite directions longitudinally of said tubular skirts,

(0) means for electrically insulating said intermediate electrode from said main electrodes when said interrupter is open and for mounting said intermediate electrode in such a position that its longitudinallyextending portions are respectively located radially inwardly of the tubular arc-running portions of said main electrodes with annular spaces therebetween constituting series-related arcing gaps,

(f) contact means operable in a closed position to conduct current between said main electrodes and movable toward an open position to establish a pair of series-related arcs in an arc-initiation region adjacent the outer ends of said skirts,

(g) and means for driving said arcs in a radially-inward direction from said arc-initiation region into said series-related arcing gaps.

11. The circuit interrupter of claim 10 in combination with means for propelling the arcs in a circumferential direction about the longitudinally-extending portions of the intermediate electrode when the arcs have reached said longitudinally extending portions.

References Cited by the Examiner UNITED STATES PATENTS 3,014,109 12/61 Burger 200147 BERNARD A. GILHEANY, Primary Examiner. ROBERT K. SCHAEFER, Examiner. 

1. A VACUUM-TYPE CIRCUIT INTERRUPTER COMPRISING: (A) A PAIR OF CUP-SHAPED ELECTRODES, EACH COMPRISING A BODY PORTION AND A TUBULAR SKIRT PROJECTING FROM SAID BODY PORTION AND TERMINATING IN AN OUTER END OF ANNULAR CONFIGURATION, (B) MEANS FOR MOUNTING SAID ELECTRODES IN SPACEDAPART RELATIONSHIP WITH SAID SKIRTS GENERALLY ALIGNED AND SAID OUTER ENDS SPACED FROM EACH OTHER, (C) EACH OF SAID CUP-SHAPED ELECTRODES FURTHER COMPRISING A TUBULAR ARC-RUNNING PORTION LOCATED RADIALLY INWARDLY OF SAID SKIRT AND MEANS ELECTRICALLY INTERCONNECTING SAID SKIRT AND SAID TUBULAR ARC-RUNNING PORTION IN SUCH A MANNER THAT CURRENT FLOWING BETWEEN SAID TUBULAR ARC-RUNNING PORTION AND SAID SKIRT IS FORCED TO FLOW THROUGH SAID OUTER END, (D) AN INTERMEDIATE ELECTRODE HAVING TWO TUBULAR PORTIONS, (E) MEANS FOR ELECTRICALLY INSULATING SAID INTERMEDIATE ELECTRODE FROM SAID CUP-SHAPED ELECTRODES WHEN SAID INTERRUPTER IS OPEN AND FOR MOUNTING SAID INNERMEDIATE ELECTRODE IN SUCH A POSITION THAT IS TUBULAR PORTIONS ARE RESPECTIVELY LOCATED RADIALLY INWARDLY OF THE TUBULAR ARC-RUNNING PORTIONS OF SAID CUP-SHAPED ELECTRODES WITH ANNULAR SPACES THEREBETWEEN CONSTITUTING SERIES-RELATED ARCING GAPS, (F) CONTACT MEANS OPERABLE IN A CLOSED POSITION TO CONDUIT CURRENT BETWEEN SAID CUP-SHAPED ELECTRODES AND MOVABLE TOWARD AN OPEN POSITION TO ESTABLISH A PAIR OF SERIES-RELATED ARCS IN AN ARC-INITIATION REGION ADJACENT THE OUTER ENDS OF SAID SKIRTS, (G) AND MEANS FOR DRIVING SAID ARCS IN A RADIALLY-INWARD DIRECTION FROM SAID ARC-INITIATION REGION INTO SAID SERIES-RELATED ARCING GAPS. 